In the past several weeks many cities in Northern China from heavy fogs and severe cold.

问题补充：

In the past several weeks, many cities in Northern China from heavy fogs and severe cold.

A. had suffered

B. have been suffering

C. were suffered

D. suffered

答案：

A. had suffered

B. have been suffering

C. were suffered

D. suffered

解析：可联系答.案.网客服索取。